Is it normal?

Question
I have an 18-1/2 yr old kitty.
One day he'll eat his food as though I haven't fed him in years,and the next day he could care less if he eats or not. Sometimes he can go 2-3 days without taking the Felovite. Then just about a month or so later, he'd start to eat one day and not the next. Then it became every 2 or 3 days.
Finally I had to start putting the Felovite in his mouth.
So is it normal for him to do this? Or could it possibly be the summer heat? Or does it mean something else is wrong?
A few months ago when he had his vaccinations, the vet thought he was doing good for his age. Now a few months later..

Answer
I don't know, what is a felovite? If it is a vitamin then I would stop giving them to him. Coupled with his food, they are probably too high in many nutrients for his age at this point.

A lot can change in an 18 yr old cat in a matter of days, let alone months. I would get him back into the vets soon. What he is showing are signs of something not being right, either his kidneys are failing or his system is having age related issues.

He needs a check up, the sooner the better.